1. Field of the Invention
The invention relates to a process for the preparation of 1,3-dichloropropane by reacting bis(3-hydroxypropyl)ether with hydrogen chloride, preferably in the presence of a tertiary basic nitrogen compound or other tertiary aliphatic base as a catalyst, distilling off the 1,3-dichloropropane and the water of reaction, and working up the two phases.
2. Background of the Invention
1,3-Dichloropropane is an important intermediate for the preparation of pharmaceuticals and agrochemicals and also serves as a low-toxic solvent. Syntheses of 1,3-dichloropropane have been known for a long time from the literature. Most start from 1,3-propanediol, reacting with thionyl chloride or phosphorus pentachloride (see Clark Streight, Trans. roy. Soc. Canada (3) 23, 3, (1929) 77).
A disadvantage of this process is the relatively high cost of the starting material 1,3-propanediol. There is, however, a great interest in a process which proceeds economically with a low-cost starting material and which is as easy to realize industrially as the customary processes for the preparation of chlorine compounds from the corresponding hydroxyl compounds.
The object of the invention was therefore to find a suitable starting material for the synthesis of 1,3-dichloropropane which is low-cost and available in a sufficient amount.
The object is achieved according to the invention by using bis(3-hydroxypropyl)ether as starting material. This etherdiol is produced as a byproduct in the production of 1,3-propanediol and which, according to EP-A-0 577 972, can only be cleaved by a specific complex process step.
Surprisingly, it has now, however, been found that under conditions under which the hydroxyl groups of the etherdiol are exchanged for chlorine atoms, the ether group is also cleaved and that 1 mol of etherdiol and 4 mol of hydrogen chloride give 2 mol of 1,3-dichloropropane and 3 mol of water according to the equation
HOCH2CH2CH2OCH2CH2CH2OH+4 HClxe2x86x922 ClCH2CH2CH2Cl+3 H2O
The invention thus provides a process for the preparation of 1,3-dichloropropane, which comprises reacting bis(3-hydroxypropyl)ether, preferably in the presence of tertiary basic nitrogen compounds or other tertiary aliphatic base, with hydrogen chloride, distilling off the 1,3-dichloropropane and water of reaction which form and working up the two phases together.
3-Chloropropanol forms as an intermediate. Bis(3-chloropropyl)ether forms in a small amount depending on the distillation conditions during the reaction. It can be returned to the reaction. The ready cleavability of the ether using hydrogen chloride is contrary to information in the literature: for example, xe2x80x9cHouben-Weylxe2x80x9d (Halogen compounds volume, Georg Thieme Verlag Stuttgart, 1962, pages 839 and 840) states that cyclic ethers, such as, for example, tetrahydrofuran and allyl ethers can be cleaved relatively easily, (but) that the saturated aliphatic ethers can only be converted into the chlorides using hydrogen chloride under extreme conditions. In addition, the monograph xe2x80x9cOrganisch-Chemische Experimentierkunstxe2x80x9d by Weygand/Hilgetag (Johann Ambrosius Barth Verlag Leipzig, 1970) states, on page 241, in connection with ether cleavage using hydrogen halides: xe2x80x9cOf the hydrogen halides, HI is particularly effective, HBr less so, HCl least soxe2x80x9d. According to this, it was thus to be assumed that the etherdiol is only just cleaved with hydrogen chloride.
The process according to the invention does not usually require a solvent. If, for whatever reason, however, it should be advantageous, possible solvents are, for example, aliphatic or aromatic hydrocarbons, halogen compounds and aliphatic ethers.
Tertiary basic nitrogen compounds acting as catalysts are advantageously used in an amount such that they adopt the function of a solvent.
Suitable tertiary basic nitrogen compounds are pyridine and alkylpyridines such as methyl-, dimethyl- and ethylpyridine, and technical-grade mixtures of these compounds (so-called pyridine bases), and also quinoline and derivatives of quinoline, such as, for example, 2-methylquinoline (quinaldine) and 4-methylquinoline (lepidine), N,N-dialkylaniline, such as N,N-dimethylaniline, and tertiary amines, such as trialkylamines and mixtures of the above compounds. Preference is given to using so-called pyridine bases. These are in the form of hydrochlorides during and after the reaction and, in this form, can be separated off easily and be used repeatedly one after the other.
In the continuous procedure, etherdiol and hydrogen chloride are added simultaneously to the reactor to the pyridine bases present as hydrochlorides, and 1,3-dichloropropane and water are distilled off.
In the presence of tertiary basic nitrogen compounds, explained using pyridine bases as an example, the procedure can be as follows:
A pyridine base mixture is introduced initially and hydrogen chloride is introduced to saturation. The etherdiol is then added, and the mixture is heated from about 20xc2x0 C. to about 120xc2x0 C. while passing in hydrogen chloride. The ratio of pyridine base to etherdiol is from 0.1 mol to 5 mol, preferably from 0.5 mol to 1.5 mol to 2 mol. The amount of hydrogen chloride depends on its rate of absorption. It is introduced at a rate such that there is always a slight excess in the reactor. In order that the reaction proceeds quickly enough, the temperature is increased to about 190xc2x0 C., preferably to 160xc2x0 C. over the course of time. During the reaction, a mixture of 1,3-dichloropropane and water is continuously distilled off. This mixture is worked up in a manner known per se, and the dichloropropane is purified by distillation.
The only partially reacted products 3-chloropropanol and bis(3-chloropropyl)ether can be returned to the reaction.
The example below serves to illustrate the process according to the invention in more detail, but does not intend to limit it to the circumstances specifically given.